The present invention relates to an apparatus for treating soil or vegetation, and which includes a carrier vehicle equipped with a support frame that is stationary in relation to the vehicle, and a boom equipped with means for treating the soil or vegetation and disposed substantially according to a disposition parallel to the soil and perpendicular to the direction of travel of the vehicle.
The phrase treatment of the soil or of the vegetation is meant to include the entire range of agricultural techniques including, for example, sowing operations.
The development of agricultural techniques has led to a significant increase in the size of the booms of spraying or other apparatuses, it being possible for the length of this boom to reach 40 meters. Various problems result from this large size and from the fact that, on the one hand, the vehicle does not move over a soil which is horizontal in its entirety and that, on the other hand, local irregularities in the surface of the soil cause the vehicle, during its motion, to be perturbed by abrupt movements which can be considered as pivoting movements about an axis parallel to the direction of travel, which direction will be called hereinafter "longitudinal" , about an axis along a direction perpendicular to the surface of the soil, which will be called hereinafter "vertical direction" and about an axis having a direction parallel to the surface of the soil and perpendicular to the direction of the travel, which will be called hereinafter "transverse direction".
The most irksome movements are pivoting movements about the longitudinal axis, and there have been known for a long time suspensions, for example of the "swinging" type or of the "rocker link" type, "having rocker links" which enable the boom to be maintained parallel to the surface of the soil during the abrupt movements of the vehicle about the longitudinal axis. Such suspensions are often associated with manual- or automatic-control adjustment means intended for fixing the best height of the boom, as far as its extremities, above the surface of the soil in such a way as to reduce the risk of one of the extremities of the boom coming into contact with the soil and running the risk of being damaged.
Work carried out for limiting the consequences of pivoting movements about a vertical axis, or "yawing", and about a transverse axis, or "pitching", has been much more limited. A yawing movement creates little risk of damaging the boom by contact with the soil but, on the other hand, it can lead, at the extremities of the boom, to over-concentrations or under-concentrations of the treatment product spread over the soil, for example. Furthermore, it causes significant forces to be experienced by the articulations which connect together successive sections of the boom and by the means for maintaining these sections in alignment.
A pitching movement can have similar consequences because the boom, no longer being maintained in a vertical plane, tilts due to its weight and to its flexibility forwards or backwards, which can also lead to over-concentrations and under-concentrations of the treatment product and to excessive flexural and torsional forces at the location of the linkages between the successive sections of the boom. Moreover, if the soil rises and falls in the direction of the path of the vehicle or, alternatively, when the carrier vehicle abruptly accelerates or decelerates, there can result from this an abnormal loading of the structure of the boom which is made to bend due to its weight and to its flexibility, in the manner mentioned hereinabove. In order to avoid the risks of breakage, provision is made for increasing the ability of the boom to withstand the flexural and torsional forces, leading to an undesirable increase in its weight and its cost.
It would be possible to envisage overcoming these drawbacks simply by replacing, in conventional so-called swinging suspensions, the longitudinal-axis articulations by ball joints permitting motion in all directions. In fact, this solution is inoperable because the extent of the angular motions which can be tolerated and which have to be compensated for is not the same about the longitudinal, transverse or vertical axes.
As regards limiting the consequences of yawing, it is possible to mention U.S. Pat. No. 4,998,025 to PATTERSON ET AL., which describes a device in which the boom is connected to the vehicle by the agency of a vertical torsion bar, which permits yawing oscillations about a vertical axis whilst providing a force for returning to the situation where the boom is in a transverse plane. The torsion bar is connected to a longitudinal pivot joint, which permits oscillations about the longitudinal axis. Damping means are provided.
In French Patent Application No. 2,559,686 to H. DELCLUSE, the torsion bar of PATTERSON ET AL. is replaced by a vertical pivot joint with elastic return means.
As regards limiting the effects of pitching, the applicant's previous U.S. Pat. No. 4,561,,591 provides for the boom to be suspended by a ball joint to a support linked to the chassis and for rolling surfaces and rollers to permit pivoting movements about a longitudinal axis. In addition, the rollers can move away from the rolling surfaces, which enables the boom to pivot about a transverse axis passing through the center of the ball joint, only in one direction. Elastic means are provided for bringing the rollers back into contact with the rolling surfaces. This disposition therefore leads only to a partial solution of the problem.
The object of the present invention is to provide an apparatus which effectively avoids the drawbacks mentioned hereinabove whilst keeping, of course, the benefit of the "swinging-", "rocker link-" or other-type suspensions of the prior art, with low-cost and robust equipment.